Transneptunian Object 1994 TG2

This photo shows the faint image (arrow) of a new transneptunian object, discovered with the ESO 3.5-metre New Technology Telescope in October 1994. It is here seen in a negative reproduction (dark stars on white sky) of the CCD frame on which it was first noticed.

It was detected because of its extremely slow motion, only 3 arcsec/hour. Six accurate positions were measured and allowed to determine an approximate distance of about 42 AU, that is 6300 million kilometres from the Sun. This is far outside the orbit of the outermost, large planet, Neptune (4500 million kilometres); hence the classification as a "transneptunian" object.

It has in the meantime been given the designation "1994 TG2" by the Minor Planet Center of the International Astronomical Union. The observed magnitude is about 24, i.e., it is about 16 million timesfainter than the faintest objects that can be perceived with the unaided eye. Its diameter is probably 100 - 200 kilometres.

1994 TG2 is the 17th transneptunian object found during the past two years. Nine of these have distances between 31 and 36 AU, the other eight between 40 and 45 AU. None have so far been found in the gap in between; this may be an effect of Neptune's gravitational attraction. Colour measurements of some of the brightest have shown that they are unusually red.

The transneptunian objects represent an entirely new class of objects in the solar system. It is not yet clear how they may be related to other minor bodies like comets and minor planets, and whether Pluto and its moon Charon, as well as the Neptunian moon Triton (which was observed from close quarters by Voyager 2 in 1989), also belong to this class.